A thin film type field-effect transistor (FET) is a basic structure in a microelectronic field. The FET includes three electrodes, that is, a source electrode, a drain electrode, and a gate electrode, an insulating layer, and a semiconductor layer. In the case of when the above semiconductor layer is a conductive channel between the two above electrodes, that is, the source electrode and the drain electrode, the FET acts as a capacitor. In the above channel, the concentration of the charge carrier is controlled by using voltage that is applied through the gate electrode. As a result, a flow of electric charges between the source electrode and the drain electrode may be controlled by voltage that is applied through the above gate electrode.
Recently, a concern has been grown rapidly about FETs using an organic semiconductor material. In the case of when the organic semiconductor material is used, electronic devices may be produced by using a printing process such as screen-printing, ink-jet printing, or micro-contact printing. In addition, in the case of when the above material is used, the process may be performed at a very low temperature of the substrate in a state where a vacuum is not required as compared to the case of when a known inorganic semiconductor material is used. Therefore, the electronic device using the organic semiconductor material including FETs may be produced under a very soft production condition at low cost as compared to the case of when the inorganic semiconductor material is used.
Studies have been conducted to use organic materials such as small molecules, polymers, and oligomers as an organic semiconductor material in FETs since the 1980s. With respect to results of studies in the above-mentioned field, in views of the charge carrier mobility in FETs, performance of the organic FET is increased from 10−5 cm2/Vs to 1 cm2/Vs (J. M. Shaw, P. F. Seidler, IBM J. Res. & Dev., Vol. 45, 3 (2001)). The performance of the organic transistor is as good as that of a current amorphous silicon transistor. Thus, the organic transistor may be applied to E-papers, smart cards, display devices or the like.
A structure of the organic transistor may be classified into a top gate structure or a bottom gate structure according to the position of the gate. As shown in FIGS. 1 and 2, the bottom gate structure may be classified into a top gate structure or a bottom gate structure according to the position of source/drain electrodes which are disposed on or under a semiconductor layer. In the organic transistor having the bottom gate structure, since the organic semiconductor layer is directly exposed to the outside, stability may be reduced. An organic semiconductor material sensitively reacts with moisture or oxygen. In particular, when oxygen and light are present simultaneously, the organic semiconductor material maybe damaged due to a photo oxidation reaction. This may cause a decrease in performance of the organic transistor. In order to avoid this, an encapsulation layer may be formed on the semiconductor layer. However, there is a problem in that in the course of forming the encapsulation layer, the organic semiconductor material may be dissolved or damaged. In addition, since the organic transistor is not used alone but used while being connected to a memory device or a display device, after the organic transistor is formed, there is a need to provide a function that is capable of protecting the organic semiconductor layer in order to perform the other processes.
[Disclosure]
[Technical Problem]
The present inventors have found that in the case of when an insulating organic material having a band gap of 3 eV or more or no portion having four pairs or more of double bonds and single bonds continuously connected is used in conjunction with a thiazolothiazole derivative in order to form an organic semiconductor layer, since the organic semiconductor layer is stable even though a separate encapsulation layer is not used, it is possible to increase resistance in respects to the outside environment while desirable performance of the organic transistor is maintained.
Therefore, it is an object of the present invention to provide a thiazolothiazole derivative, an organic transistor that includes an organic semiconductor layer containing an insulating organic material having a band gap of 3 eV or more or no portion having four pairs or more of double bonds and single bonds continuously connected, and a method of producing the same.
[Technical Solution]
The present invention provides an organic transistor that includes an organic semiconductor layer containing a thiazolothiazole derivative having a structural unit represented by the following Formula 1 and an insulating organic material having a band gap of 3 eV or more or no portion having four pairs or more of double bonds and single bonds continuously connected:

wherein x, y, and y are a ratio of structural units, x is a real number with 0<x≦1, y is a real number with 0≦y<1, z is a real number with 0≦z<1, and x+y+z=1,
n is an integer in the range of 1 to 1,000, and more preferably 10 to 1,000,
Ar and Ar′ are the same as or different from each other, and are independently a bivalent cyclic or non-cyclic hydrocarbon group having a conjugated structure, or a bivalent heterocyclic group having a conjugated structure,
A and B are the same as or different from each other, and are independently a bivalent cyclic or non-cyclic hydrocarbon group having a conjugated structure, a bivalent heterocyclic group having a conjugated structure, or an acyclic group as follows:

wherein R′ and R″ are the same as or different from each other, and may be independently a hydrogen atom; a halogen atom; a linear, branched, or cyclic alkyl group; a linear, branched, or cyclic alkoxy group; a thioalkoxy group; a nitrile group; a nitro group; an amino group; a substituted or unsubstituted aryl group, or a substituted or unsubstituted heteroaryl group, and a dotted line is a portion linked to a main chain of Formula 1.
[Advantageous Effects]
According to the present invention, since a mixture of an insulating organic material having a band gap of 3 eV or more or no portion having four pairs or more of double bonds and single bonds continuously connected and a thiazolothiazole derivative is used in order to form an organic semiconductor layer of an organic transistor, it is possible to increase resistance in respects to the outside environment while desirable performance of the organic transistor is maintained even though a separate encapsulation layer is not used.